Eleven healthy men (22 ± 2.2 years) were evaluated. The heart rate and R-R intervals (R-Ri) were recorded in a sitting position during spontaneous breathing and NPPV application (600 min each). The NPPV was delivered using a bi-level positive airway pressure (BiPAP) applied via a nasal mask with inspiratory and expiratory levels of 20 and 13 cmH2O, respectively. The heart rate and its variability were analyzed in the time domain by the RMSSD (root mean square of the squares of the differences between successive R-Ri) and SDNN (standard deviation of all R-Ri) indexes of R-Ri (ms); and in the frequency domain by the low-frequency (LF) and high-frequency (HF), in normalized units (nu), and the LF/HF ratio. For statistical analysis, the paired t test was used with a level of significance of 5%.